Primary cultures of adrenal medulla cells will be used to investigate cellular and molecular events concerned with stimulus-secretion coupling and other aspects of adrenal medulla function. Radioligand binding studies will be used to characterize the muscarinic and nicotinic receptors on the plasma membrane and their interaction with various agonist and antagonists determined. These studies will provide a better understanding of the site of action of various secretory antagonists and the interaction of muscarinic and nicotinic agonists on the same cell. A simplified model system using cells permeabilized by treatment with digitonin will be developed. This system may enable the identification and characterization of intracellular components involved in stimulus-secretion coupling. The role of Na+:Ca++ countertransport and energy-dependent Ca++-pumping in terminating agonist-stimulated catecholamine secretion will be elucideated. The presence of a Ca++-activated Mg++-ATPase in the plasma membrane will be investigated and its molecular properties and physiological defined. The primary cultures also provide a good model system to better characterize the uptake 1 system for transport of catecholamines across the plasma membrane and to study the role of secretory agonists in regulating its activity. The regulation of catecholamine biosynthesis will also be investigated. These studies are not only relevant to the adrenal medulla but also to the physiology and function of the sympathetic nervous system.